Data is not comeing from proxies to master-server. I tested with db syncer turned on and off both on every proxy host and on server

ps ax | grep "db syncer"
99788 ?? SN 0:00,09 zabbix_proxy: db syncer [sleeping for 5 seconds] (zabbix_proxy)
But that gave little effect. Latest data updates once after proxy's db recreated and stalls after that.

Not a word in log files about why that happens.